You could write a book about pro's & cons about carbon and what it does for bow performance. Like Bill was saying above, there are many different kinds of carbon lay ups, and types. it's typically a series of pre-preg layers that make up a matrix.....and there are different types of Unidirectional carbon composites too.
Some limb designs use a carbon weave matrix, or a 45/45 lay up using unidirectional carbon. This helps stability a lot, which is a huge part of performance, but adds nothing to the arrow speed. Other limb designs using Uni directional carbon directly on the back of the limbs can increase the speed significantly, but it's a trade off in stability, and will not work on some limbs at all....Uni carbon has less torsional stability than glass by far.
Carbon is a real love / hate thing for most bowyers. Very expensive stuff, tricky to work with, and it takes years to come up with the right carbon for the right limb design.....
There are experienced carbon limb builders that have great results.Zipper, Dryad, Border, Centaur, and the list goes on... have got this stuff dialed in nicely. But they've invested thousands and thousands in finding just the right lay up for just the right limb design.....
Bottom line is that "Performance" isn't measured just by arrow speed alone. Velocity is only one part of over all performance, and not the most important factor at all. There are some very nice bows out there being built with, & without the use of carbon composites.